The present invention relates to stairway constructions and, more particularly, to prefabricated curvilinear stairway constructions adapted to be mounted to curvilinear walls having differing degrees of curvature.
The fitting and assembly of stairways to curvilinear walls presents problems which are unique and do not exist where the stairways are to be mounted to flat planar wall surfaces. One such problem is the difficulty of mounting prefabricated stairway units on such curvilinear walls. This is because prefabricated constructions have components which are usually of fixed, predetermined dimensions. However, structures having curvilinear walls, such as the walls on cylindrical tanks and grain bins, frequently vary over wide ranges of curvature between given installations. For example, grain bins may have diameters of curvature of anywhere between 15 to 105 feet or more, Conversely, the planarity of flat wall surfaces is constant between different installations and, therefore, are readily adapted to accommodate prefabricated constructions having components of predetermined dimensions.
A few proposals have been made in the past for prefabricated stairway constructions which are adapted to be mounted to structures having curvilinear walls. One such prefabricated construction is shown in U.S. Pat. No. 4,143,740. In that construction, a plurality of modular stairway units of predetermined length are provided which have substantially straight side stringers and slotted connector plates attach consecutive ones of the stringers of the respective units together as the stair is assembled. In such construction, the individual stringers remain substantially straight after assembly. As a result, a gap of varying size, depending upon the degree of curvature of the wall, is present between the outside stringers. The slotted connector plates are provided to bridge this gap so that the stringers of the respective modular units may be attached together. Thus, in essence, each of the stairway units in the construction disclosed in U.S. Pat. No. 4,143,740 remains substantially linear in plan view and when the units are connected together and mounted to the curvilinear wall, they form a polygonal outline, in plan, each of the modular unit segments forming a straight segment of the polygon as the stair rises over the height of the structure.
Such prior prefabricated stairway construction has several disadvantages. One disadvantage is that assembly is complicated by the presence of substantial numbers of parts, such as the additional connector plates and bolts which are needed to bridge the gap between the adjacent stringers. Another disadvantage is the gap itself which is formed in such straight segment constructions. This gap increasingly varies in size from the end of the steps nearer the wall to the outer ends which are spaced from the wall. This gap may be of substantial size where the aforementioned prior stair construction is to be mounted to a wall having a high degree of curvature, i.e. a short diameter of curvature. The varying size of this gap from inside to outside of the stair and its maximum size itself may present a safety hazard for personnel using the stairs.
In order to overcome this gap problem prefabricated stair constructions have been proposed in which the stair assembly more closely approximates the curvilinearity of the wall to avoid the polygonal nature of the stairway construction shown in the aforementioned patent and, thereby, reduce the gap existing between the stairs. However, such constructions are substantially more difficult to assemble to the wall because they have a substantially greater number of pieces and they usually require the simultaneous alignment of a large number of pieces before the pieces can be bolted or otherwise fixed together.
The present invention has the purpose of overcoming these several disadvantages in the prior curvilinear stairway constructions. The stairway constructions incorporating the principles of the present invention may be formed of elements which are all straight during and following manufacture, but which may be bent during assembly and mounting to the wall to be substantially concentric to the curvature of the wall to which they are mounted. Thus, because all of the elements of the stairway construction of the present invention are initially straight, they are easy to manufacture, store, ship to the site of assembly, and to handle during assembly. The stairway constructions incorporating the principles of the present invention, even though initially formed of all straight elements, are capable of substantially reducing the gap which may be present between the steps of the stairway upon assembly of the stairway to walls having a high degree of curvature. Moreover, the constructions of the present invention may be prefabricated, but are readily adapted to fit curvilinear walls even though the diameter of curvature of these walls may vary over a wide range without the need to provide parts especially dimensioned for each given diameter of curvature. The stairway constructions incorporating the principles of the present invention may be assembled to rise either in the right of left direction also without the need to provide parts unique to either of those directions, and are capable of fitting standard structures, such as grain bins, such that the stairway construction of the present invention may be mounted to preexisting bolt holes and using preexisting bolts in the structure without the need to provide additional drilling operations during the course of assembly of the stairway construction. The stairway constructions incorporating the principles of the present invention substantially minimize the number of pieces in the assembly which must be put together, the number of bolt or other fastening means which must be provided, the steps involved in attaching the several pieces together, and the number of elements which must be simultaneously aligned with each other at any given time during the course of assembly. Finally, elements of the stairway construction incorporating the principles of the present invention may be readily reinforced to minimize the weight and thickness of materials used to form these elements and, yet, are readily capable of being firmly assembled together and of easy and rapid adjustment to accommodate a wide range of differing degrees of wall curvature.
In one principal aspect of the present invention, a curvilinear stairway construction for mounting to a curvilinear wall includes first and second stringer means which are elongate members mountable one above the other and which, when unmounted, are substantially straight over their length. Step means includes inner and outer ends and first mounting means mounts the outer ends of at least one of the step means to each of the first and second stringer means at a location spaced from the ends of the stringer means. Second mounting means mounts the inner ends of the step means to the curvilinear wall. The step means cause the first and second stringer means to bend substantially uniformly over their length such that the curvature of the stringer means is substantially concentric to the curvilinear wall when the step means are mounted to the stringer means and to the curvilinear wall, respectively, by the first and second mounting means. Third mounting means mounts the upper end of the first stringer means directly to the lower end of the second stringer means.
In another principal aspect of the present invention, the aforementioned stairway construction includes a plurality of spaced apertures in the upper and lower ends of the first and second stringer means which may be selectively aligned with each other to allow adjustable mounting of the stringer means to each other to adjust for varying degrees of curvature of the curvilinear wall.
In still another aspect of the present invention, reinforcing means are located adjacent the longitudinal edges of the first and second stringer means to reinforce the construction.
These and other objects, features and advantages of the present invention will become readily understood upon a consideration of the following detailed description.